MCP Spec Defaults Mean Silent Tools Are Treated as Destructive by Compliant Clients
Under the Model Context Protocol schema, any tool that ships without a destructiveHint annotation is not simply silent — by documented default, clients honoring the spec must treat it as potentially destructive. Developer Eugeniya Ivanova highlighted this during a ChatGPT app directory review walkthrough published on September 7, 2026, where an automated scanner flagged four read-only tools lacking explicit destructiveHint values, prompting her to add destructiveHint: false without changing the tools themselves. A week earlier, on August 30, 2026, Himanshu Kumar audited a deployed server with six tools carrying zero annotations, summarizing the issue as: the server did not lie — it simply said nothing. The schema's ToolAnnotations interface defines defaults for four boolean fields, but a NOTE within the same spec warns clients never to base tool-use decisions on annotations from untrusted servers, creating a tension between the two rules. The result is that the same absent annotation can be interpreted differently by fully compliant clients, depending on which part of the specification they prioritize.
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